ArcObjects 10.1 IPixelFilter (IClipFilter) not filtering for IMosaicDataset

Question

I am attempting to extract an irregular polygon from a Mosaic Dataset using ArcObjects in C#. This sample shows how to open a mosaic dataset in ArcObjects. Referencing existing (VB) code, this snippet is from a working tool which uses IPixelOperation to reduce the raster to only the portion covered by a polygon:

Dim pRaster As IRaster = pRasLayer.Raster
Dim pPixOp As IPixelOperation = pRaster
Dim pShapeWS As IWorkspace = pShapeWSfact.OpenFromFile(pFolderPath, 0)
Dim pShapeFws As IFeatureWorkspace = pShapeWS
Dim pShapeFC As IFeatureClass = pShapeFws.OpenFeatureClass(pFileName & ".shp")
Dim pFeatCur As IFeatureCursor = pShapeFC.Search(Nothing, True)
Dim pFeat As IFeature = pFeatCur.NextFeature
Dim pClipFilter As IClipFilter = New ClipFilterClass()
Dim pGeom As IGeometry

Do Until pFeat Is Nothing
  pGeom = pFeat.ShapeCopy
  If pGeom.SpatialReference.FactoryCode <> pMap.SpatialReference.FactoryCode Then pGeom.Project(pMap.SpatialReference)
  pClipFilter.Add(pGeom)

  pFeat = pFeatCur.NextFeature
Loop
pPixOp.PixelFilter = pClipFilter

Which illustrates how an IClipFilter can be used to restrict the display of a raster... I am attempting to use IClipFilter as IPixelFilter to return the irregular portion of a raster within a polygon:

IMosaicWorkspaceExtensionHelper mosaicExtHelper = new MosaicWorkspaceExtensionHelperClass();
IMosaicWorkspaceExtension mosaicExt = mosaicExtHelper.FindExtension(gMosDSsrcWorkspace);
IMosaicDataset pMosDS = mosaicExt.OpenMosaicDataset(gMosDSname);
IRasterDataset3 pInDS = (IRasterDataset3)pMosDS;
IRaster pInRaster = pInDS.CreateFullRaster();
IPixelOperation pPixOp = (IPixelOperation)pInRaster;

IClipFilter pClipFilter = new ClipFilterClass();
// add some geometries to the clip filter, in the same spatial reference as the raster
pPixOp.PixelFilter = (IPixelFilter) pClipFilter;

// then read/write the raster
IPnt ReadBlockSize = new PntClass();
IPnt SrcUpperLeft = new PntClass();
IPnt DestUpperLeft = new PntClass();

// create the pixel block for read/write
ReadBlockSize.SetCoords(pDestCols, RowsToRead);
IPixelBlock pReadBlock = pInRaster.CreatePixelBlock(ReadBlockSize);
IRasterEdit pWriteEdit = (IRasterEdit)pWriteRaster;
for (int RowMin = 0; RowMin < pDestRows; RowMin += RowsToRead)
{
    SrcUpperLeft.SetCoords(pSrcColOffset, pSrcRowOffset + RowMin);
    DestUpperLeft.SetCoords(0, RowMin);
    pInRaster.Read(SrcUpperLeft, pReadBlock);
    //(pClipFilter as IPixelFilter).Filter(pReadBlock);// tried this too, but it still didn't work
    pWriteEdit.Write(DestUpperLeft, pReadBlock); 
}

The result:

The image is the size of the dataset which is correct but the pixels are unfiltered. Does IPixelOperation, IClipFilter only work in ArcMap or with IRasterLayer? Do I need to supply the geometries in cell coordinates? Is there an updated/different interface required to work with an IMosaicDataset?... I've tried several different combinations of readers/writers/filterers and none of them seem to have any affect - What am I missing?

Answer 1

In ArcMap the MosaicDataset is a MosaicLayer and is essentially a CompositeLayer, and the actual raster image is one of its components. So find the raster in the MosaicLayer and treat it exactly as you did the raster in your first example...

Dim pEnumLayer As IEnumLayer = My.ArcMap.Document.FocusMap.Layers(Nothing, True)
pEnumLayer.Reset()
Dim pLayer As ILayer = pEnumLayer.Next()

Do Until pLayer Is Nothing
    If TypeOf pLayer Is IMosaicLayer Then
        Dim pCompositeLayer As ICompositeLayer = pLayer
        Dim pRasterLayer As IRasterLayer = pCompositeLayer.Layer(2)
        Dim pRaster As IRaster = pRasterLayer.Raster
        Dim pPixOp As IPixelOperation = pRaster
        Dim pShapeWSfact As IWorkspaceFactory = New ShapefileWorkspaceFactory
        Dim pShapeWS As IWorkspace = pShapeWSfact.OpenFromFile("P:\", 0)
        Dim pShapeFws As IFeatureWorkspace = pShapeWS
        Dim pShapeFC As IFeatureClass = pShapeFws.OpenFeatureClass("RasterClipTest.shp")
        Dim pFeatCur As IFeatureCursor = pShapeFC.Search(Nothing, True)
        Dim pFeat As IFeature = pFeatCur.NextFeature()
        Dim pClipFilter As IClipFilter = New ClipFilterClass()
        Dim pGeom As IGeometry
        Do Until pFeat Is Nothing
            pGeom = pFeat.ShapeCopy
            If pGeom.SpatialReference.FactoryCode <> My.ArcMap.Document.ActiveView.FocusMap.SpatialReference.FactoryCode Then
                pGeom.Project(My.ArcMap.Document.FocusMap.SpatialReference)
            End If
            pClipFilter.Add(pGeom)
            pFeat = pFeatCur.NextFeature
        Loop
        pPixOp.PixelFilter = pClipFilter
        My.ArcMap.Document.ActiveView.Refresh()
        Exit Do
    End If
    pLayer = pEnumLayer.Next()
Loop

There a few ways you could find the raster in the MosaicLayer, and the one I did above is to assume it is at index 2, though I'm not positive this always the case. Another way would be to find the layer in the MosaicLayer named "Image", but again I am not positive that it will always have that name, since I have not extensively used mosaic datasets and thoroughly tested them.

Edit 5/8/15: This is another way to get the raster of the MosaicDataset, based on the comments below. This seems to only work in ArcMap, however, and not in the standalone windows form...

Dim WSF As IWorkspaceFactory = New FileGDBWorkspaceFactory
Dim fgdbWorkspace As IWorkspace = WSF.OpenFromFile("P:\misc.gdb", 0)
Dim pMosaicHelper As IMosaicWorkspaceExtensionHelper = New MosaicWorkspaceExtensionHelperClass()
Dim pMosaicExt As IMosaicWorkspaceExtension = pMosaicHelper.FindExtension(fgdbWorkspace)
Dim pMosaicDataset As IMosaicDataset = pMosaicExt.OpenMosaicDataset("MD")
Dim pRasterLayer As IRasterLayer = New RasterLayer
pRasterLayer.CreateFromDataset(pMosaicDataset)
pRasterLayer.Name = "my raster layer"
My.ArcMap.Document.FocusMap.AddLayer(pRasterLayer)
Dim pRaster As IRaster = pRasterLayer.Raster
Dim pPixOp As IPixelOperation = pRaster
Dim pShapeWSfact As IWorkspaceFactory = New ShapefileWorkspaceFactory
Dim pShapeWS As IWorkspace = pShapeWSfact.OpenFromFile("P:\", 0)
Dim pShapeFws As IFeatureWorkspace = pShapeWS
Dim pShapeFC As IFeatureClass = pShapeFws.OpenFeatureClass("RasterClipTest.shp")
Dim pFeatCur As IFeatureCursor = pShapeFC.Search(Nothing, True)
Dim pFeat As IFeature = pFeatCur.NextFeature()
Dim pClipFilter As IClipFilter = New ClipFilterClass()
Dim pGeom As IGeometry
Do Until pFeat Is Nothing
    pGeom = pFeat.ShapeCopy
    If pGeom.SpatialReference.FactoryCode <> My.ArcMap.Document.ActiveView.FocusMap.SpatialReference.FactoryCode Then
        pGeom.Project(My.ArcMap.Document.FocusMap.SpatialReference)
    End If
    pClipFilter.Add(pGeom)
    pFeat = pFeatCur.NextFeature
Loop
pPixOp.PixelFilter = pClipFilter